Heating unit



FIG. 1 is a top plan view of a heating unit, showing my new design;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a right side elevational view thereof.

The rear surface of the heating unit, is substantially planar and unornamented. 

The ornamental design for the heating unit, as shown and described. 